I hope you're well.
In regards to your question related to wifi calling, this is a process that happens beyond the control of the AP or the ZD. Nor does the ZD or the AP take part in this feature as this is treated as regular traffic.
New controllers such as SmartZone or Cloud, offer wifi calling traffic recognition and they apply QoS settings to this traffic, but they still do not interfere with the wifi calling process.
I recommend you verify network connectivity towards the carrier's ePDG, as the wifi calling communication relies on the connectivity between the client and the gateway.
Please let me know if you had any questions.
Orlando Elias | Technical Support Engineer